SHORE PROTECTION WORKS FOR THE COAST

INTRODUCTION

The site visit revealed that the existing seawall has been considerably damaged .At several locations ,the slope of the seawall was steeper than even 1:1,which is mainly due to scour at the toe of the seawall. There were further a few pockets where deposition of sand was observed.

PROPOSALS TO COUNTER THE EXISTING EROSION

Option 1 :SEAWALL

Option 1a :(Conventional)

It was observed from the site visit that the existing seawall lacks filter layer, which is required to avoid scouring at the toe and also to avoid seepage. Hence it is proposed to have a filter layer of 300 mm thick. Moreover , in most of the portions the secondary armour layer is exposed , hence a primary layer consisting of armour stones of size ranging from 1-2 T with a slope of 1:3 and to a crest elevation of +5.5m.

Option 1b : (Gabion boxes)

In addition to the strengthening of secondary armour layer with stones of size 1-2T ,and a filter bed of 300 mm thick ,the seawall can be further strengthened by using Gabion boxes of size 2.5mx1mx1m,filled with smaller size stones and laid at a slope of 1:3 with a crest elevation of +5.5m.The Gabion boxes will act as a primary layer and also increases the stability of the seawall against the failure due to sliding.

Option 1c : ( Gabion at Toe)

In this option the toe of the seawall is protected with gabion boxes laid above the filter bed to increase the stability of the toe against the toe failure. Armour stones of size ranging from 1-2T are laid over the existing cross section at a slope of 1:3 to a crest elevation of up to +5.5m,which will act as a primary layer.

Option 2 :GROINS

Option 2a :(Transitional groin field)

The stretch of the coast of 3 KM approx, along the study area can be protected by a transitional groin field consisting of 11 groins with an average length of about 200 m.

Option 2b : (Transitional T-groins)

Instead of the traditional transitional groin field ,the above stretch can be protected with T-groins ,whereby the accumulation of the sand can be faster. The Transitional T-Groin field will be consisted of 11 T-groins with an average length of 200 m.